The present invention relates to a device for electrophysiologically localising target areas in the brain, in accordance with the preamble of patent claim 1.
With the increasing average age of the population in the industrial nations, the incidence of age-related illnesses is also growing. Parkinson""s syndrome and essential tremor certainly figure among the most common and most debilitating illnesses here. Once medicinal treatments no longer show any success, such neurodegenerative illnesses are treated by brain surgery, the success of which is highly dependent on correctly determining the target area in the brain. For a while now, target areas have often been localised using electrophysiological efferences of the neuronal discharge pattern along a stereotactically given trajectory. For this purpose, multi-channel microprobes are used which are inserted into the patient""s brain by means of a manipulator and which at their active end comprise a multitude of tightly packed microelectrodes arranged axially in rows, via which electrophysiological efferences are obtained in the target area. Exactly determining the target in this way is extremely important, for a misplaced therapeutic measure can have serious side effects for the patient. Performing a pallidotomy on a Parkinson""s patient is cited here as an example, wherein a misplaced coagulation electrode would result in irreversible damage to the tractus opticus in the immediate vicinity of the pallidum. Alongside the continuing Parkinson""s symptoms, the patient in question would then additionally suffer from a possibly considerable restriction of his vision.
Admittedly, functional areas in the brain can in principle be localised with the aid of hitherto known microprobe localising techniques, however even experienced brain surgeons require a number of processes with a test probe to obtain a reasonably correct image of the layers of the structure of the target areas. It is however also known from practice many brain surgeons have little or no experience of identifying areas from their specific activities. According to the level of difficulty, such a traditional approach, introducing the probe a number of times, lasts between 6 and 20 hours. For a large part of this time, the patient has to be conscious, so the success of the electrical stimulation can be checked by way of absence of the illness. A further disadvantage are of course the repeatedly necessary penetrations of the substance of the brain.
With respect to the prior art regarding microprobes and medical navigation systems (see below), reference is made to the following documents: U.S. Pat. Nos. 5,855,801; U.S. 5,843,148; U.S. 5,833,709; U.S. 5,800,535; U.S. 5,782,645; U.S. 5,755,759; U.S. 5,713,922; U.S. 5,524,619; U.S. 5,524,338; U.S. 5,496,369; U.S. 5,411,540; U.S. 5,388,577; U.S. 5,215,088; U.S. 4,969,468; U.S. 4,890,623; U.S. 4,837,049; U.S. 4,461,304.
It is the object of the present invention to provide a device for electrophysiologically localising target areas in the brain, which does not exhibit the disadvantages cited above. In particular, a high precision of the target finding method in the sub-millimeter range is to be achieved, and the surgeon is to be given fundamental and comprehensible assistance in using the captured efference data.
This object is solved in accordance with the invention by assigning the microprobe a tracking device which allows the microprobe to be positionally detected by means of a neuronavigation system. In particular, this has the advantage that with such a device, electrophysiological localising can be planned and also carried out with a much higher initial precision by means of the microprobe, and thus with a smaller number of insertion processes and in much shorter time. The number of required trajectories is minimised, which also makes the localising process as a whole minimally invasive. Neuronavigation offers various options both in calculating the target co-ordinates and in operative surgery. The target is localised on the one hand by physiologically identifying the target area by means of the microprobe, and on the other by anatomical navigation.
In a preferred embodiment of the present invention, the navigation system comprises a screen output on which the evaluations of electrophysiological localization and of the navigational data are shown together. The electrophysiological data in question (such as efferences or spike frequencies) can then be shown for the surgeon, together with anatomical image data available to the navigation system, in a unified representation and including a databank. This improves the operating technique, and the risk to the patient is minimized. Neuronavigation systems, such as are known for example from DE 196 39 615 C2, work with patient data recorded beforehand by tomographic imaging methods, for example CT or MR recording methods. Via the screen output, images reconstructed from these data can be displayed together with images of the microprobe itself and its results data, and the surgeon can then compare the peak model of the electrophysiological navigation, which offers an individual neurone resolution, with the image information and with theoretical knowledge, to exactly determine the position of the microprobe or of a microelectrode on it. The invention thus combines the two localizing methods into navigation with high resolution using a user-friendly and easy-to-use user interface.
In accordance with an advantageous embodiment, the microprobe has 25 to 32 microelectrodes. If 32 tightly packed microelectrodes are present at the active end of the microprobe, it is possible to pass through a target area completely and relatively quickly with the microprobe and then to simultaneously derive nerve signals as neuronal discharge from each of the 32 microelectrodes patterns from various brain centre segments.
In accordance with an embodiment in accordance with the invention, the navigation system is an optical navigation system, the tracking device being attached to a manipulator for the microprobe and consisting of an arrangement of markers, in particular of three reflection markers, whose spatial position is detected by cameras of the navigation system.
On the other hand, it is possible to provide magnetic navigation, i.e. a navigation system which is designed as a magnetic navigation system, the tracking device being attached to a manipulator for the microprobe or to the microprobe itself and consisting of an arrangement of coils, in particular of two miniature coils, whose spatial position is detected in an established magnetic field.
In the two cases cited above, it is advantageous if the navigation system further comprises a patient tracking device, by means of which a current position of the patient""s head can be detected in real time, such that movements of the patient do not have a disruptive or precision-blunting effect on navigation or localisation.
The two localising systems, namely the electrophysiological localising system with the microprobe and the neuronavigation system, can supplement each other and so provide synergistic effects. Thus, the device in accordance with the invention is on the one hand advantageously designed such that the navigation system comprises a computer unit which links the data from the electrophysiological efferences of functional areas of the brain, the advance of the probe and the navigational data with one another and adapts navigation by way of positional data and information from the electrophysiological efferences of functional areas of the brain. In this way, the navigation system can benefit from the very high precision of electrophysiological localisation, and other anatomical points can be very exactly assigned by way of this precise information. A second option is to design the device in accordance with the invention such that the navigation system comprises a computer unit which links the data from the electrophysiological efferences of functional areas of the brain and the navigational data with each other and works positional data and information from the electrophysiological efferences of functional areas of the brain into the anatomical data available to the navigation system. In this way, for example, a xe2x80x9cvirtual brain atlasxe2x80x9d for the given patient can be produced, which is available for later treatments or diagnoses.
In general terms, the present invention makes it possible to detect specific functional areas of the brain, either for conventional surgery, for a so-called deep brain simulation (DBS) or for neurological examinations. In this sense, the invention also relates to the methods described herein, while simultaneously using multi-channel microprobes and a navigation system, wherein visualising and equalising the databank with image data produced beforehand from tomographic imaging methods have the advantageous effect of combination.